The present invention relates generally to keying systems of electronic musical instruments and more particularly to a keying system of simplified circuitry in an electronic organ in which a harmonic synthesis system is used.
An electronic musical instrument, in general, is so constituted and adapted as to carry out the functions of electronically generating a sound source signal, turning this signal "ON" or "OFF" or controlling the amplitude thereof in response to manipulation of keyboard, obtaining a signal having a frequency corresponding to the keyboard and a musical tone waveform having harmonics (higher harmonics) spectrum, and converting this signal into sound.
The factors which determine the tone color of an electronic musical instrument are essentially: (a) the manner in which harmonics are included; (b) the variations with time (envelopes) of the levels of the fundamental tone and the harmonics; (c) noise, distortion, and dynamic range; and (d) other sound field effects. Of these factors, the factor (a), the manner in which harmonics are included, is important, and the greater the number of harmonics included, the more colorful and fuller is the tone color obtained.
A conventional synthesis type organ in which a sine-wave synthesis system is used produces musical tones by suitably synthesizing 9 harmonics from the 1/2 harmonic to the 8th harmonic. In an organ of this synthesis type, harmonic adjusters operated by draw bars and comprising variable resistors are provided and used to adjust the levels of the synthesized harmonics thereby to variably adjust the tone color.
In an organ of this synthesis type, however, the number of gate circuits required for signal "ON-OFF" operation in response to keyboard manipulation has been the product of the number of the keys and the number of the harmonic adjusters. For example, in the case of 49 keys and 9 harmonic adjusters, 49.times.9=441 gate circuits are required. Ordinarily, for a single gate circuit, approximately 10 components such as transistors, diodes, resistors, and capacitors are required. Accordingly, a total of some 4,400 components are required in this organ. As a consequence, a conventional synthesis type organ has been accompanied by the problems of complicated circuitry, large required number of components, and high price.
Furthermore, in order to change the envelope for each harmonic, it has been necessary to increase the number of harmonic series of different envelopes together with the number of gate circuits for exclusive use thereof or to use a circuit organization wherein switching is carried out by a gang switch between ordinary envelope circuits and attack envelope forming circuits. Consequently, this gives rise to further complication of the circuit organization.
Another conventional electronic organ is the organ of bright-wave type wherein a Formant system is used. In this bright-wave type organ, a signal of a waveform containing in abundant harmonics of waves such as saw-tooth waves and pulse waves is used as a sound source signal, and the manner in which these harmonics are contained is adjusted by means such as filters thereby to obtain tones of the desired tone color. However, the signal of the above described waveform contains only odd harmonics and does not contain even harmonics. For this reason, the tone color of this organ is monotonic in comparison with that of the synthesis type organ. Furthermore, it is very difficult to design the filters used for determining the manner in which the harmonics are contained so that they will have ideally sharp characteristics.